CVE-2023-26562 in Zimbra Collaboration Suite
Summary
by MITRE • 02/13/2024
In Zimbra Collaboration (ZCS) 8.8.15 and 9.0, a closed account (with 2FA and generated passwords) can send e-mail messages when configured for Imap/smtp.
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Analysis
by VulDB Data Team • 10/28/2024
The vulnerability identified as CVE-2023-26562 affects Zimbra Collaboration Suite versions 8.8.15 and 9.0, specifically impacting the authentication and authorization mechanisms within the IMAP and SMTP protocols. This security flaw allows closed or disabled accounts to maintain the ability to send email messages through these protocols, creating a significant bypass of intended access controls. The issue is particularly concerning because it affects accounts that have been properly disabled or closed, yet still retain the capability to transmit messages through email servers that support IMAP and SMTP authentication methods. The vulnerability stems from improper validation of account status during the authentication process, where the system fails to properly verify that an account is active and enabled before granting email sending privileges.
The technical implementation of this vulnerability involves a failure in the account state validation mechanism within the Zimbra server's authentication layer. When an account is closed or disabled through the administrative interface, the system should revoke all access permissions including email sending capabilities through IMAP and SMTP protocols. However, in affected versions, the authentication process does not adequately check the account status against the account's enabled/disabled state, allowing authenticated but closed accounts to continue operating within the email infrastructure. This behavior represents a direct violation of the principle of least privilege and demonstrates a critical flaw in the access control implementation. The vulnerability is classified as a privilege escalation issue under CWE-284 which specifically addresses inadequate access control mechanisms, and it aligns with ATT&CK technique T1078.004 which covers valid accounts with restricted permissions being used to perform unauthorized actions.
The operational impact of this vulnerability extends beyond simple unauthorized email sending capabilities. It creates a potential vector for abuse where compromised or malicious actors could leverage closed accounts to send spam, phishing emails, or other malicious content without detection. The presence of two-factor authentication and generated passwords adds complexity to the threat model, as attackers who gain access to these credentials could potentially use them to send messages from closed accounts without triggering additional security alerts. This vulnerability undermines the security posture of organizations relying on Zimbra, particularly those with strict email governance policies where disabled accounts should be completely isolated from email operations. The risk is amplified in environments where email monitoring and compliance requirements are stringent, as closed accounts may not be properly tracked or audited for continued email activity.
Organizations should immediately implement mitigations including applying the latest security patches released by Zimbra to address this vulnerability. The patch addresses the core authentication logic by ensuring proper account state validation before granting email sending permissions through IMAP and SMTP protocols. Additionally, administrators should conduct comprehensive audits of their email systems to identify any closed accounts that may still be active or have access to email services. Network segmentation and monitoring solutions should be enhanced to detect unusual email patterns originating from accounts that should be disabled. Implementing additional authentication controls such as IP address restrictions, rate limiting, and enhanced logging of email operations can provide additional layers of defense. The vulnerability also highlights the importance of regular security assessments and vulnerability scanning to identify similar issues within email infrastructure, as this type of access control bypass can potentially affect other components of the email system that rely on similar authentication patterns. Organizations should also consider implementing automated account lifecycle management processes that ensure proper disabling and cleanup of accounts across all email protocols to prevent similar issues from occurring in the future.